/*
 * Copyright (c) 2003, 2013, Oracle and/or its affiliates. All rights reserved.
 * ORACLE PROPRIETARY/CONFIDENTIAL. Use is subject to license terms.
 *
 *
 *
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 *
 *
 *
 *
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 *
 *
 *
 *
 */
package java.util.jar;

import java.util.SortedMap;
import java.io.InputStream;
import java.io.OutputStream;
import java.io.File;
import java.io.IOException;
import java.beans.PropertyChangeListener;


/**
 * Transforms a JAR file to or from a packed stream in Pack200 format. Please refer to Network
 * Transfer Format JSR 200 Specification at <a href=http://jcp.org/aboutJava/communityprocess/review/jsr200/index.html>http://jcp.org/aboutJava/communityprocess/review/jsr200/index.html</a>
 * <p> Typically the packer engine is used by application developers to deploy or host JAR files on
 * a website. The unpacker  engine is used by deployment applications to transform the byte-stream
 * back to JAR format. <p> Here is an example using  packer and unpacker:
 * <pre>{@code
 *    import java.util.jar.Pack200;
 *    import java.util.jar.Pack200.*;
 *    ...
 *    // Create the Packer object
 *    Packer packer = Pack200.newPacker();
 *
 *    // Initialize the state by setting the desired properties
 *    Map p = packer.properties();
 *    // take more time choosing codings for better compression
 *    p.put(Packer.EFFORT, "7");  // default is "5"
 *    // use largest-possible archive segments (>10% better compression).
 *    p.put(Packer.SEGMENT_LIMIT, "-1");
 *    // reorder files for better compression.
 *    p.put(Packer.KEEP_FILE_ORDER, Packer.FALSE);
 *    // smear modification times to a single value.
 *    p.put(Packer.MODIFICATION_TIME, Packer.LATEST);
 *    // ignore all JAR deflation requests,
 *    // transmitting a single request to use "store" mode.
 *    p.put(Packer.DEFLATE_HINT, Packer.FALSE);
 *    // discard debug attributes
 *    p.put(Packer.CODE_ATTRIBUTE_PFX+"LineNumberTable", Packer.STRIP);
 *    // throw an error if an attribute is unrecognized
 *    p.put(Packer.UNKNOWN_ATTRIBUTE, Packer.ERROR);
 *    // pass one class file uncompressed:
 *    p.put(Packer.PASS_FILE_PFX+0, "mutants/Rogue.class");
 *    try {
 *        JarFile jarFile = new JarFile("/tmp/testref.jar");
 *        FileOutputStream fos = new FileOutputStream("/tmp/test.pack");
 *        // Call the packer
 *        packer.pack(jarFile, fos);
 *        jarFile.close();
 *        fos.close();
 *
 *        File f = new File("/tmp/test.pack");
 *        FileOutputStream fostream = new FileOutputStream("/tmp/test.jar");
 *        JarOutputStream jostream = new JarOutputStream(fostream);
 *        Unpacker unpacker = Pack200.newUnpacker();
 *        // Call the unpacker
 *        unpacker.unpack(f, jostream);
 *        // Must explicitly close the output.
 *        jostream.close();
 *    } catch (IOException ioe) {
 *        ioe.printStackTrace();
 *    }
 * }</pre>
 * <p> A Pack200 file compressed with gzip can be hosted on HTTP/1.1 web servers. The deployment
 * applications can use "Accept-Encoding=pack200-gzip". This indicates to the server that the client
 * application desires a version of the file encoded with Pack200 and further compressed with gzip.
 * Please refer to  <a href="{@docRoot}/../technotes/guides/deployment/deployment-guide/pack200.html">Java
 * Deployment Guide</a> for more details and techniques. <p> Unless otherwise noted, passing a
 * <tt>null</tt> argument to a constructor or method in this class will cause a {@link
 * NullPointerException} to be thrown.
 *
 * @author John Rose
 * @author Kumar Srinivasan
 * @since 1.5
 */
public abstract class Pack200 {

  private Pack200() {
  } //prevent instantiation

  // Static methods of the Pack200 class.

  /**
   * Obtain new instance of a class that implements Packer.
   * <ul>
   * <li><p>If the system property <tt>java.util.jar.Pack200.Packer</tt>
   * is defined, then the value is taken to be the fully-qualified name
   * of a concrete implementation class, which must implement Packer.
   * This class is loaded and instantiated.  If this process fails
   * then an unspecified error is thrown.</p></li>
   *
   * <li><p>If an implementation has not been specified with the system
   * property, then the system-default implementation class is instantiated,
   * and the result is returned.</p></li>
   * </ul>
   *
   * <p>Note:  The returned object is not guaranteed to operate
   * correctly if multiple threads use it at the same time.
   * A multi-threaded application should either allocate multiple
   * packer engines, or else serialize use of one engine with a lock.
   *
   * @return A newly allocated Packer engine.
   */
  public synchronized static Packer newPacker() {
    return (Packer) newInstance(PACK_PROVIDER);
  }


  /**
   * Obtain new instance of a class that implements Unpacker.
   * <ul>
   * <li><p>If the system property <tt>java.util.jar.Pack200.Unpacker</tt>
   * is defined, then the value is taken to be the fully-qualified
   * name of a concrete implementation class, which must implement Unpacker.
   * The class is loaded and instantiated.  If this process fails
   * then an unspecified error is thrown.</p></li>
   *
   * <li><p>If an implementation has not been specified with the
   * system property, then the system-default implementation class
   * is instantiated, and the result is returned.</p></li>
   * </ul>
   *
   * <p>Note:  The returned object is not guaranteed to operate
   * correctly if multiple threads use it at the same time.
   * A multi-threaded application should either allocate multiple
   * unpacker engines, or else serialize use of one engine with a lock.
   *
   * @return A newly allocated Unpacker engine.
   */

  public static Unpacker newUnpacker() {
    return (Unpacker) newInstance(UNPACK_PROVIDER);
  }

  // Interfaces

  /**
   * The packer engine applies various transformations to the input JAR file,
   * making the pack stream highly compressible by a compressor such as
   * gzip or zip. An instance of the engine can be obtained
   * using {@link #newPacker}.
   *
   * The high degree of compression is achieved
   * by using a number of techniques described in the JSR 200 specification.
   * Some of the techniques are sorting, re-ordering and co-location of the
   * constant pool.
   * <p>
   * The pack engine is initialized to an initial state as described
   * by their properties below.
   * The initial state can be manipulated by getting the
   * engine properties (using {@link #properties}) and storing
   * the modified properties on the map.
   * The resource files will be passed through with no changes at all.
   * The class files will not contain identical bytes, since the unpacker
   * is free to change minor class file features such as constant pool order.
   * However, the class files will be semantically identical,
   * as specified in
   * <cite>The Java&trade; Virtual Machine Specification</cite>.
   * <p>
   * By default, the packer does not change the order of JAR elements.
   * Also, the modification time and deflation hint of each
   * JAR element is passed unchanged.
   * (Any other ZIP-archive information, such as extra attributes
   * giving Unix file permissions, are lost.)
   * <p>
   * Note that packing and unpacking a JAR will in general alter the
   * bytewise contents of classfiles in the JAR.  This means that packing
   * and unpacking will in general invalidate any digital signatures
   * which rely on bytewise images of JAR elements.  In order both to sign
   * and to pack a JAR, you must first pack and unpack the JAR to
   * "normalize" it, then compute signatures on the unpacked JAR elements,
   * and finally repack the signed JAR.
   * Both packing steps should
   * use precisely the same options, and the segment limit may also
   * need to be set to "-1", to prevent accidental variation of segment
   * boundaries as class file sizes change slightly.
   * <p>
   * (Here's why this works:  Any reordering the packer does
   * of any classfile structures is idempotent, so the second packing
   * does not change the orderings produced by the first packing.
   * Also, the unpacker is guaranteed by the JSR 200 specification
   * to produce a specific bytewise image for any given transmission
   * ordering of archive elements.)
   * <p>
   * In order to maintain backward compatibility, the pack file's version is
   * set to accommodate the class files present in the input JAR file. In
   * other words, the pack file version will be the latest, if the class files
   * are the latest and conversely the pack file version will be the oldest
   * if the class file versions are also the oldest. For intermediate class
   * file versions the corresponding pack file version will be used.
   * For example:
   * If the input JAR-files are solely comprised of 1.5  (or  lesser)
   * class files, a 1.5 compatible pack file is  produced. This will also be
   * the case for archives that have no class files.
   * If the input JAR-files contains a 1.6 class file, then the pack file
   * version will be set to 1.6.
   * <p>
   * Note: Unless otherwise noted, passing a <tt>null</tt> argument to a
   * constructor or method in this class will cause a {@link NullPointerException}
   * to be thrown.
   * <p>
   *
   * @since 1.5
   */
  public interface Packer {

    /**
     * This property is a numeral giving the estimated target size N
     * (in bytes) of each archive segment.
     * If a single input file requires more than N bytes,
     * it will be given its own archive segment.
     * <p>
     * As a special case, a value of -1 will produce a single large
     * segment with all input files, while a value of 0 will
     * produce one segment for each class.
     * Larger archive segments result in less fragmentation and
     * better compression, but processing them requires more memory.
     * <p>
     * The size of each segment is estimated by counting the size of each
     * input file to be transmitted in the segment, along with the size
     * of its name and other transmitted properties.
     * <p>
     * The default is -1, which means the packer will always create a single
     * segment output file. In cases where extremely large output files are
     * generated, users are strongly encouraged to use segmenting or break
     * up the input file into smaller JARs.
     * <p>
     * A 10Mb JAR packed without this limit will
     * typically pack about 10% smaller, but the packer may require
     * a larger Java heap (about ten times the segment limit).
     */
    String SEGMENT_LIMIT = "pack.segment.limit";

    /**
     * If this property is set to {@link #TRUE}, the packer will transmit
     * all elements in their original order within the source archive.
     * <p>
     * If it is set to {@link #FALSE}, the packer may reorder elements,
     * and also remove JAR directory entries, which carry no useful
     * information for Java applications.
     * (Typically this enables better compression.)
     * <p>
     * The default is {@link #TRUE}, which preserves the input information,
     * but may cause the transmitted archive to be larger than necessary.
     */
    String KEEP_FILE_ORDER = "pack.keep.file.order";


    /**
     * If this property is set to a single decimal digit, the packer will
     * use the indicated amount of effort in compressing the archive.
     * Level 1 may produce somewhat larger size and faster compression speed,
     * while level 9 will take much longer but may produce better compression.
     * <p>
     * The special value 0 instructs the packer to copy through the
     * original JAR file directly, with no compression.  The JSR 200
     * standard requires any unpacker to understand this special case
     * as a pass-through of the entire archive.
     * <p>
     * The default is 5, investing a modest amount of time to
     * produce reasonable compression.
     */
    String EFFORT = "pack.effort";

    /**
     * If this property is set to {@link #TRUE} or {@link #FALSE}, the packer
     * will set the deflation hint accordingly in the output archive, and
     * will not transmit the individual deflation hints of archive elements.
     * <p>
     * If this property is set to the special string {@link #KEEP}, the packer
     * will attempt to determine an independent deflation hint for each
     * available element of the input archive, and transmit this hint separately.
     * <p>
     * The default is {@link #KEEP}, which preserves the input information,
     * but may cause the transmitted archive to be larger than necessary.
     * <p>
     * It is up to the unpacker implementation
     * to take action upon the hint to suitably compress the elements of
     * the resulting unpacked jar.
     * <p>
     * The deflation hint of a ZIP or JAR element indicates
     * whether the element was deflated or stored directly.
     */
    String DEFLATE_HINT = "pack.deflate.hint";

    /**
     * If this property is set to the special string {@link #LATEST},
     * the packer will attempt to determine the latest modification time,
     * among all the available entries in the original archive or the latest
     * modification time of all the available entries in each segment.
     * This single value will be transmitted as part of the segment and applied
     * to all the entries in each segment, {@link #SEGMENT_LIMIT}.
     * <p>
     * This can marginally decrease the transmitted size of the
     * archive, at the expense of setting all installed files to a single
     * date.
     * <p>
     * If this property is set to the special string {@link #KEEP},
     * the packer transmits a separate modification time for each input
     * element.
     * <p>
     * The default is {@link #KEEP}, which preserves the input information,
     * but may cause the transmitted archive to be larger than necessary.
     * <p>
     * It is up to the unpacker implementation to take action to suitably
     * set the modification time of each element of its output file.
     *
     * @see #SEGMENT_LIMIT
     */
    String MODIFICATION_TIME = "pack.modification.time";

    /**
     * Indicates that a file should be passed through bytewise, with no
     * compression.  Multiple files may be specified by specifying
     * additional properties with distinct strings appended, to
     * make a family of properties with the common prefix.
     * <p>
     * There is no pathname transformation, except
     * that the system file separator is replaced by the JAR file
     * separator '/'.
     * <p>
     * The resulting file names must match exactly as strings with their
     * occurrences in the JAR file.
     * <p>
     * If a property value is a directory name, all files under that
     * directory will be passed also.
     * <p>
     * Examples:
     * <pre>{@code
     *     Map p = packer.properties();
     *     p.put(PASS_FILE_PFX+0, "mutants/Rogue.class");
     *     p.put(PASS_FILE_PFX+1, "mutants/Wolverine.class");
     *     p.put(PASS_FILE_PFX+2, "mutants/Storm.class");
     *     # Pass all files in an entire directory hierarchy:
     *     p.put(PASS_FILE_PFX+3, "police/");
     * }</pre>
     */
    String PASS_FILE_PFX = "pack.pass.file.";

    /// Attribute control.

    /**
     * Indicates the action to take when a class-file containing an unknown
     * attribute is encountered.  Possible values are the strings {@link #ERROR},
     * {@link #STRIP}, and {@link #PASS}.
     * <p>
     * The string {@link #ERROR} means that the pack operation
     * as a whole will fail, with an exception of type <code>IOException</code>.
     * The string
     * {@link #STRIP} means that the attribute will be dropped.
     * The string
     * {@link #PASS} means that the whole class-file will be passed through
     * (as if it were a resource file) without compression, with  a suitable warning.
     * This is the default value for this property.
     * <p>
     * Examples:
     * <pre>{@code
     *     Map p = pack200.getProperties();
     *     p.put(UNKNOWN_ATTRIBUTE, ERROR);
     *     p.put(UNKNOWN_ATTRIBUTE, STRIP);
     *     p.put(UNKNOWN_ATTRIBUTE, PASS);
     * }</pre>
     */
    String UNKNOWN_ATTRIBUTE = "pack.unknown.attribute";

    /**
     * When concatenated with a class attribute name,
     * indicates the format of that attribute,
     * using the layout language specified in the JSR 200 specification.
     * <p>
     * For example, the effect of this option is built in:
     * <code>pack.class.attribute.SourceFile=RUH</code>.
     * <p>
     * The special strings {@link #ERROR}, {@link #STRIP}, and {@link #PASS} are
     * also allowed, with the same meaning as {@link #UNKNOWN_ATTRIBUTE}.
     * This provides a way for users to request that specific attributes be
     * refused, stripped, or passed bitwise (with no class compression).
     * <p>
     * Code like this might be used to support attributes for JCOV:
     * <pre><code>
     *     Map p = packer.properties();
     *     p.put(CODE_ATTRIBUTE_PFX+"CoverageTable",       "NH[PHHII]");
     *     p.put(CODE_ATTRIBUTE_PFX+"CharacterRangeTable", "NH[PHPOHIIH]");
     *     p.put(CLASS_ATTRIBUTE_PFX+"SourceID",           "RUH");
     *     p.put(CLASS_ATTRIBUTE_PFX+"CompilationID",      "RUH");
     * </code></pre>
     * <p>
     * Code like this might be used to strip debugging attributes:
     * <pre><code>
     *     Map p = packer.properties();
     *     p.put(CODE_ATTRIBUTE_PFX+"LineNumberTable",    STRIP);
     *     p.put(CODE_ATTRIBUTE_PFX+"LocalVariableTable", STRIP);
     *     p.put(CLASS_ATTRIBUTE_PFX+"SourceFile",        STRIP);
     * </code></pre>
     */
    String CLASS_ATTRIBUTE_PFX = "pack.class.attribute.";

    /**
     * When concatenated with a field attribute name,
     * indicates the format of that attribute.
     * For example, the effect of this option is built in:
     * <code>pack.field.attribute.Deprecated=</code>.
     * The special strings {@link #ERROR}, {@link #STRIP}, and
     * {@link #PASS} are also allowed.
     *
     * @see #CLASS_ATTRIBUTE_PFX
     */
    String FIELD_ATTRIBUTE_PFX = "pack.field.attribute.";

    /**
     * When concatenated with a method attribute name,
     * indicates the format of that attribute.
     * For example, the effect of this option is built in:
     * <code>pack.method.attribute.Exceptions=NH[RCH]</code>.
     * The special strings {@link #ERROR}, {@link #STRIP}, and {@link #PASS}
     * are also allowed.
     *
     * @see #CLASS_ATTRIBUTE_PFX
     */
    String METHOD_ATTRIBUTE_PFX = "pack.method.attribute.";

    /**
     * When concatenated with a code attribute name,
     * indicates the format of that attribute.
     * For example, the effect of this option is built in:
     * <code>pack.code.attribute.LocalVariableTable=NH[PHOHRUHRSHH]</code>.
     * The special strings {@link #ERROR}, {@link #STRIP}, and {@link #PASS}
     * are also allowed.
     *
     * @see #CLASS_ATTRIBUTE_PFX
     */
    String CODE_ATTRIBUTE_PFX = "pack.code.attribute.";

    /**
     * The unpacker's progress as a percentage, as periodically
     * updated by the unpacker.
     * Values of 0 - 100 are normal, and -1 indicates a stall.
     * Progress can be monitored by polling the value of this
     * property.
     * <p>
     * At a minimum, the unpacker must set progress to 0
     * at the beginning of a packing operation, and to 100
     * at the end.
     */
    String PROGRESS = "pack.progress";

    /**
     * The string "keep", a possible value for certain properties.
     *
     * @see #DEFLATE_HINT
     * @see #MODIFICATION_TIME
     */
    String KEEP = "keep";

    /**
     * The string "pass", a possible value for certain properties.
     *
     * @see #UNKNOWN_ATTRIBUTE
     * @see #CLASS_ATTRIBUTE_PFX
     * @see #FIELD_ATTRIBUTE_PFX
     * @see #METHOD_ATTRIBUTE_PFX
     * @see #CODE_ATTRIBUTE_PFX
     */
    String PASS = "pass";

    /**
     * The string "strip", a possible value for certain properties.
     *
     * @see #UNKNOWN_ATTRIBUTE
     * @see #CLASS_ATTRIBUTE_PFX
     * @see #FIELD_ATTRIBUTE_PFX
     * @see #METHOD_ATTRIBUTE_PFX
     * @see #CODE_ATTRIBUTE_PFX
     */
    String STRIP = "strip";

    /**
     * The string "error", a possible value for certain properties.
     *
     * @see #UNKNOWN_ATTRIBUTE
     * @see #CLASS_ATTRIBUTE_PFX
     * @see #FIELD_ATTRIBUTE_PFX
     * @see #METHOD_ATTRIBUTE_PFX
     * @see #CODE_ATTRIBUTE_PFX
     */
    String ERROR = "error";

    /**
     * The string "true", a possible value for certain properties.
     *
     * @see #KEEP_FILE_ORDER
     * @see #DEFLATE_HINT
     */
    String TRUE = "true";

    /**
     * The string "false", a possible value for certain properties.
     *
     * @see #KEEP_FILE_ORDER
     * @see #DEFLATE_HINT
     */
    String FALSE = "false";

    /**
     * The string "latest", a possible value for certain properties.
     *
     * @see #MODIFICATION_TIME
     */
    String LATEST = "latest";

    /**
     * Get the set of this engine's properties.
     * This set is a "live view", so that changing its
     * contents immediately affects the Packer engine, and
     * changes from the engine (such as progress indications)
     * are immediately visible in the map.
     *
     * <p>The property map may contain pre-defined implementation
     * specific and default properties.  Users are encouraged to
     * read the information and fully understand the implications,
     * before modifying pre-existing properties.
     * <p>
     * Implementation specific properties are prefixed with a
     * package name associated with the implementor, beginning
     * with <tt>com.</tt> or a similar prefix.
     * All property names beginning with <tt>pack.</tt> and
     * <tt>unpack.</tt> are reserved for use by this API.
     * <p>
     * Unknown properties may be ignored or rejected with an
     * unspecified error, and invalid entries may cause an
     * unspecified error to be thrown.
     *
     * <p>
     * The returned map implements all optional {@link SortedMap} operations
     *
     * @return A sorted association of property key strings to property values.
     */
    SortedMap<String, String> properties();

    /**
     * Takes a JarFile and converts it into a Pack200 archive.
     * <p>
     * Closes its input but not its output.  (Pack200 archives are appendable.)
     *
     * @param in a JarFile
     * @param out an OutputStream
     * @throws IOException if an error is encountered.
     */
    void pack(JarFile in, OutputStream out) throws IOException;

    /**
     * Takes a JarInputStream and converts it into a Pack200 archive.
     * <p>
     * Closes its input but not its output.  (Pack200 archives are appendable.)
     * <p>
     * The modification time and deflation hint attributes are not available,
     * for the JAR manifest file and its containing directory.
     *
     * @param in a JarInputStream
     * @param out an OutputStream
     * @throws IOException if an error is encountered.
     * @see #MODIFICATION_TIME
     * @see #DEFLATE_HINT
     */
    void pack(JarInputStream in, OutputStream out) throws IOException;

    /**
     * Registers a listener for PropertyChange events on the properties map.
     * This is typically used by applications to update a progress bar.
     *
     * <p> The default implementation of this method does nothing and has
     * no side-effects.</p>
     *
     * <p><b>WARNING:</b> This method is omitted from the interface
     * declaration in all subset Profiles of Java SE that do not include
     * the {@code java.beans} package. </p>
     *
     * @param listener An object to be invoked when a property is changed.
     * @see #properties
     * @see #PROGRESS
     * @deprecated The dependency on {@code PropertyChangeListener} creates a significant impediment
     * to future modularization of the Java platform. This method will be removed in a future
     * release. Applications that need to monitor progress of the packer can poll the value of the
     * {@link #PROGRESS PROGRESS} property instead.
     */
    @Deprecated
    default void addPropertyChangeListener(PropertyChangeListener listener) {
    }

    /**
     * Remove a listener for PropertyChange events, added by
     * the {@link #addPropertyChangeListener}.
     *
     * <p> The default implementation of this method does nothing and has
     * no side-effects.</p>
     *
     * <p><b>WARNING:</b> This method is omitted from the interface
     * declaration in all subset Profiles of Java SE that do not include
     * the {@code java.beans} package. </p>
     *
     * @param listener The PropertyChange listener to be removed.
     * @see #addPropertyChangeListener
     * @deprecated The dependency on {@code PropertyChangeListener} creates a significant impediment
     * to future modularization of the Java platform. This method will be removed in a future
     * release.
     */
    @Deprecated
    default void removePropertyChangeListener(PropertyChangeListener listener) {
    }
  }

  /**
   * The unpacker engine converts the packed stream to a JAR file.
   * An instance of the engine can be obtained
   * using {@link #newUnpacker}.
   * <p>
   * Every JAR file produced by this engine will include the string
   * "<tt>PACK200</tt>" as a zip file comment.
   * This allows a deployer to detect if a JAR archive was packed and unpacked.
   * <p>
   * Note: Unless otherwise noted, passing a <tt>null</tt> argument to a
   * constructor or method in this class will cause a {@link NullPointerException}
   * to be thrown.
   * <p>
   * This version of the unpacker is compatible with all previous versions.
   *
   * @since 1.5
   */
  public interface Unpacker {

    /**
     * The string "keep", a possible value for certain properties.
     *
     * @see #DEFLATE_HINT
     */
    String KEEP = "keep";

    /**
     * The string "true", a possible value for certain properties.
     *
     * @see #DEFLATE_HINT
     */
    String TRUE = "true";

    /**
     * The string "false", a possible value for certain properties.
     *
     * @see #DEFLATE_HINT
     */
    String FALSE = "false";

    /**
     * Property indicating that the unpacker should
     * ignore all transmitted values for DEFLATE_HINT,
     * replacing them by the given value, {@link #TRUE} or {@link #FALSE}.
     * The default value is the special string {@link #KEEP},
     * which asks the unpacker to preserve all transmitted
     * deflation hints.
     */
    String DEFLATE_HINT = "unpack.deflate.hint";


    /**
     * The unpacker's progress as a percentage, as periodically
     * updated by the unpacker.
     * Values of 0 - 100 are normal, and -1 indicates a stall.
     * Progress can be monitored by polling the value of this
     * property.
     * <p>
     * At a minimum, the unpacker must set progress to 0
     * at the beginning of a packing operation, and to 100
     * at the end.
     */
    String PROGRESS = "unpack.progress";

    /**
     * Get the set of this engine's properties. This set is
     * a "live view", so that changing its
     * contents immediately affects the Packer engine, and
     * changes from the engine (such as progress indications)
     * are immediately visible in the map.
     *
     * <p>The property map may contain pre-defined implementation
     * specific and default properties.  Users are encouraged to
     * read the information and fully understand the implications,
     * before modifying pre-existing properties.
     * <p>
     * Implementation specific properties are prefixed with a
     * package name associated with the implementor, beginning
     * with <tt>com.</tt> or a similar prefix.
     * All property names beginning with <tt>pack.</tt> and
     * <tt>unpack.</tt> are reserved for use by this API.
     * <p>
     * Unknown properties may be ignored or rejected with an
     * unspecified error, and invalid entries may cause an
     * unspecified error to be thrown.
     *
     * @return A sorted association of option key strings to option values.
     */
    SortedMap<String, String> properties();

    /**
     * Read a Pack200 archive, and write the encoded JAR to
     * a JarOutputStream.
     * The entire contents of the input stream will be read.
     * It may be more efficient to read the Pack200 archive
     * to a file and pass the File object, using the alternate
     * method described below.
     * <p>
     * Closes its input but not its output.  (The output can accumulate more elements.)
     *
     * @param in an InputStream.
     * @param out a JarOutputStream.
     * @throws IOException if an error is encountered.
     */
    void unpack(InputStream in, JarOutputStream out) throws IOException;

    /**
     * Read a Pack200 archive, and write the encoded JAR to
     * a JarOutputStream.
     * <p>
     * Does not close its output.  (The output can accumulate more elements.)
     *
     * @param in a File.
     * @param out a JarOutputStream.
     * @throws IOException if an error is encountered.
     */
    void unpack(File in, JarOutputStream out) throws IOException;

    /**
     * Registers a listener for PropertyChange events on the properties map.
     * This is typically used by applications to update a progress bar.
     *
     * <p> The default implementation of this method does nothing and has
     * no side-effects.</p>
     *
     * <p><b>WARNING:</b> This method is omitted from the interface
     * declaration in all subset Profiles of Java SE that do not include
     * the {@code java.beans} package. </p>
     *
     * @param listener An object to be invoked when a property is changed.
     * @see #properties
     * @see #PROGRESS
     * @deprecated The dependency on {@code PropertyChangeListener} creates a significant impediment
     * to future modularization of the Java platform. This method will be removed in a future
     * release. Applications that need to monitor progress of the unpacker can poll the value of the
     * {@link #PROGRESS PROGRESS} property instead.
     */
    @Deprecated
    default void addPropertyChangeListener(PropertyChangeListener listener) {
    }

    /**
     * Remove a listener for PropertyChange events, added by
     * the {@link #addPropertyChangeListener}.
     *
     * <p> The default implementation of this method does nothing and has
     * no side-effects.</p>
     *
     * <p><b>WARNING:</b> This method is omitted from the interface
     * declaration in all subset Profiles of Java SE that do not include
     * the {@code java.beans} package. </p>
     *
     * @param listener The PropertyChange listener to be removed.
     * @see #addPropertyChangeListener
     * @deprecated The dependency on {@code PropertyChangeListener} creates a significant impediment
     * to future modularization of the Java platform. This method will be removed in a future
     * release.
     */
    @Deprecated
    default void removePropertyChangeListener(PropertyChangeListener listener) {
    }
  }

  // Private stuff....

  private static final String PACK_PROVIDER = "java.util.jar.Pack200.Packer";
  private static final String UNPACK_PROVIDER = "java.util.jar.Pack200.Unpacker";

  private static Class<?> packerImpl;
  private static Class<?> unpackerImpl;

  private synchronized static Object newInstance(String prop) {
    String implName = "(unknown)";
    try {
      Class<?> impl = (PACK_PROVIDER.equals(prop)) ? packerImpl : unpackerImpl;
      if (impl == null) {
        // The first time, we must decide which class to use.
        implName = java.security.AccessController.doPrivileged(
            new sun.security.action.GetPropertyAction(prop, ""));
        if (implName != null && !implName.equals("")) {
          impl = Class.forName(implName);
        } else if (PACK_PROVIDER.equals(prop)) {
          impl = com.sun.java.util.jar.pack.PackerImpl.class;
        } else {
          impl = com.sun.java.util.jar.pack.UnpackerImpl.class;
        }
      }
      // We have a class.  Now instantiate it.
      return impl.newInstance();
    } catch (ClassNotFoundException e) {
      throw new Error("Class not found: " + implName +
          ":\ncheck property " + prop +
          " in your properties file.", e);
    } catch (InstantiationException e) {
      throw new Error("Could not instantiate: " + implName +
          ":\ncheck property " + prop +
          " in your properties file.", e);
    } catch (IllegalAccessException e) {
      throw new Error("Cannot access class: " + implName +
          ":\ncheck property " + prop +
          " in your properties file.", e);
    }
  }

}
